1. Field of the Invention
The present invention relates to an ink jet recording head, a method for producing the same and a recording apparatus equipped therewith.
2. Related Background Art
The ink jet recording method, forming a record by generating small ink droplets and depositing such droplets onto a recording material such as paper, is featured by extremely low noise at the recording operation, ability of achieving high-speed recording and ability of recording on plain paper. Among such ink jet recording, particular attention is being paid to so-called bubble jet recording method utilizing an energy generating member for generating energy for ink discharge.
FIGS. 11A, 11B, 12A and 12B illustrate the representative film structure of a heater portion and an electric connection portion in the recording head for the above-mentioned bubble jet recording.
FIGS. 11A and 11B show a heater board 100 of the bubble jet recording head, connected by wire bonding to a substrate (wiring substrate) for receiving an electrical signal from the printer. On an Si substrate 101, there is formed a heat accumulation layer 102, on which formed are a heat-generating element (electrical resistance layer) 103 for generating the ink discharging energy and a wiring (wiring electrode layer) 104 for supplying the heat-generating element with the electrical signal, with thin film forming technology. The heater board 100 is completed by forming thereon an insulation film 105 and a cavitation layer 106. The electrical connection with the wiring substrate is achieved by bonding a wire 109, with a wire bonding device, to a contact pad 111 provided in a contact hole (through hole) 107 which is opened in the protective layer.
FIGS. 12A and 12B show another method of electrical connection in the bubble jet recording apparatus, in which an ink discharging element and a TAB tape are connected by the TAB method. On an Si substrate 101, there is formed a heat accumulation layer 102, on which formed are a heat-generating element 103 for generating the ink discharging energy and a wiring 104 for supplying the heat-generating element with the electrical signal, by thin film forming technology. On these layers, an insulation film 105 is formed, and a contact hole 107 is formed for electrically connecting the heat-generating wiring 104 with an electrical connection layer formed on top. Then a cavitation layer 106 and an electrical connection layer 110 are formed for example by sputtering, and an electrical connection pad 111 is formed by photolithographic method. The electrical connection is achieved by bonding the electrical connection pad 111 of the completed heater board 100 and a lead 112 of a TAB tape by a bonding device.
In case the electrical connection pad is positioned in a recessed part (through hole) as shown in FIGS. 11A and 11B, the pad area has to be made large in order that the bonding is not hindered by the surrounding layers (insulation layer etc.). However, the area of the electrical connection pad cannot be made large enough, because a large number of functional elements are positioned on the substrate of the ink jet recording head and also because the dimension of the recording head is made smaller in recent years. For this reason, there is adopted a method of forming a bump of a conductive material on the through hole, thereby forming the electrical connection pad higher than the surrounding insulation layer. In either of the electrical connecting methods mentioned above, the surface of the electrical connection pad is desirably not concave but provided with a sufficiently large flat area, in order to increase the adhesion strength of bonding. However, if the bump is formed on the pad portion for example by sputtering, the film of the bump follows the stepped surface shape of the through hole whereby the surface of the bump is recessed. On the other hand, in case the bump is formed by electroplating in the through hole, the electroplating has to be conducted after the through hole portion is covered with a conductive film of a high anticorrosive property such as TiW, in order to prevent that aluminum constituting the wiring electrode is dissolved in the electroplating operation. For this reason, the formed conductive film follows the stepped shape of the through hole also in this case, whereby the surface of the bump becomes recessed. Besides, in order to effect such electroplating operation, there has to be provided a current supplying wiring for electroplating, in a part of the wiring electrode or of the conductive film.
Also the surface of the electrical connection pad can be made flat by extending the wiring from the through hole to the end of the substrate as shown in FIGS. 12A and 12B, such configuration does not match the aforementioned tendency of compactization of the substrate.
In the recording head of the side shooter type, there can be adopted the TAB connection shown in FIGS. 12A and 12B, but such electrical connecting method based on TAB requires an additional gold layer by sputtering or evaporation on the electrical connection layer 110 on the substrate, in comparison with the conventional wire bonding method, thus leading to the following drawbacks of:
1) requiring additional apparatus for gold film formation and patterning;
2) requiring an additional mask for the additional patterning step; and
3) requiring a larger target for a large-sized wafer, with a significantly increased initial investment of the gold for such a target.
In consideration of the foregoing, an object of the present invention is to provide an ink jet recording head and a producing method therefor, enabling size reduction of the recording head and providing excellent reliability in the connection with the external wiring.
Another object of the present invention is to provide an ink jet recording head and a producing method therefor, based on an electrical connecting method capable of solving the above-mentioned drawbacks 1), 2) and 3) and applicable both to the edge shooter type and the side shooter type, with a high production yield, a high process throughput and a low cost.
The above-mentioned objects can be attained, according to the present invention, by an ink jet recording head provided with a heat-generating resistance layer for generating thermal energy used for ink discharge, and a wiring electrode layer electrically connected to the heat-generating resistance layer, also provided on a substrate with an electrothermal converting element, an insulating protective layer covering the electrothermal converting element, and an external electrical connection portion electrically connected to the electrothermal converting element and to be adhered to an external wiring for applying a voltage to the electrothermal converting element, wherein the external electrical connection portion is formed by a film grown by electroless plating from the wiring electrode layer through a through hole formed in the insulating protective layer. The above-mentioned ink jet recording head further includes the features that an anticavitation Ta layer is formed on the insulating protective layer, avoiding the position of the external electrical connection portion, that a photosensitive resin layer constituting walls of a liquid path is formed on the insulating protective layer, that the external wiring is constituted by a TAB tape, and that the substrate has a protruding portion between the external electrical connection portion and the end of the substrate.
According to the present invention, there is also provided a method for producing an ink jet recording head provided with a heat-generating resistance layer for generating thermal energy used for ink discharge, and a wiring electrode layer electrically connected to the heat-generating resistance layer, also provided on a substrate with an electrothermal converting element, an insulating protective layer covering the electrothermal converting element, and an external electrical connection portion electrically connected to the electrothermal converting element and to be adhered to an external wiring for applying a voltage to the electrothermal converting element, the method comprising a step of forming a through hole in the insulating protective layer thereby partially exposing the wiring electrode layer, and a step of growing a film from the exposed wiring electrode layer by electroless plating thereby forming the external electrical connection portion. The above-mentioned method for producing the ink jet recording head further includes the features that an anticavitation Ta layer is formed on the insulating protective layer, avoiding the position of the external electrical connection portion, that the step of forming the external electrical connection portion by electroless plating is conducted after providing a photosensitive resin layer constituting the walls of a liquid path on the insulating protective layer, that the step of forming the external electrical connection portion by electroless plating is conducted forming the Ta layer and anodizing the surface thereof, that the external wiring is constituted by a TAB tape, that the substrate has a protruding portion between the external electrical connection portion and the end of the substrate, and that the protruding portion is formed simultaneously with the formation of the photosensitive resin layer constituting the liquid path walls.
According to the present invention, there is further provided a recording apparatus comprising the above-mentioned ink jet recording head.
According to the present invention, since the electroless plated film constituting the external electrical connection portion is grown solely from the portion exposed in the through hole, the surface of the electroless plated film is not recessed but can provide a flat area, whereby high reliability in the adhesion with the external wiring can be secured in the ink jet recording head. Also such configuration is suitable for a compact ink jet recording head, since the external electrical connection portion need not be extended.
Furthermore, the film configuration employed in the conventional electrical connection by wire bonding can be adopted without change, and nickel and gold can be formed by mere immersion in plating liquid, solely on the aluminum portion exposed by opening the contact hole. Furthermore, the configuration of the present invention is applicable also to the ink jet recording head of the side shooter type, since the electrical connection can be achieved with the TAB tape.